I have a rather complex MongoDB Operator that uses a where to look through multiple users to see if they have a certain value, and if so it changes the value of it. My problem is that the value it checks for can be different for different cases, so my $set would require me to add strings together to get the property that I would change. This is what I mean:
users.update({$where:function() {
return this.profile.chatInfo.subscribedRooms.hasOwnProperty(findChatroom._id);
}},{$set: {"profile.chatInfo.subscribedRooms."+findChatroom._id:false}},{multi:true}
)
The only thing that does not work in that code is the part in the $set where I add "profile.chatInfo.subscribedRooms."+findChatroom._id
Another thing I have tried was making a variable that was equal to those strings added, and use the variable, but it also didn't work.
var addedString = "profile.chatInfo.subscribedRooms."+findChatroom._id;
users.update({$where:function() {
return this.profile.chatInfo.subscribedRooms.hasOwnProperty(findChatroom._id);
}},{$set: {addedString:false}},{multi:true}
)
What I am actually trying to do here, is that whenever a chat message is sent, this operator is ran. It looks for every user that is subscribed to a room, and sets the value to false. The value being true or false just refers to whether or not the user has read the chat. This is to be used for notifications.
Edit: My question is not a duplicate of this because the MongoDB set command works differently from simply changing the value of an object's property. To add onto that, MongoDB can't even use the notation of object[property], because the docs say the only way to access embedded fields is through dot notation.
Actually those links that #BlakesSeven provided will solve your problem. It should be something like this,
var addedString = "profile.chatInfo.subscribedRooms."+findChatroom._id;
var $set = {};
$set[addedString] = false;
users.update({$where:function() {
return this.profile.chatInfo.subscribedRooms.hasOwnProperty(findChatroom._id);
}}, { $set: $set }, { multi:true })
Related
Does anyone know of a good way (either natively in MongoDB or through Mongoose) to "unset" a document property when it's empty?
Use case: I have an optional secondary email address field. It's not a required field and it defaults to undefined. But once it's populated, I'm finding it difficult to clear the value again.
I'd normally use a pre-save middleware, but when using transactions, those don't seem to fire.
The behavior I'd like is that whenever the value is false-y (empty string, null, etc.) it should be unset from the document.
I've thought of writing static methods into my various schema to purge some of these fields, but that seems heavy-handed
I hope this is the thing that you looking for
let filters = [ null,false, "undefined",""];
db.collectionName.updateOne({
optionalEmail: {
"$in":filters
}
}, {
"$unset": {
optioanlEmail: ""
}
});
Update: I use "$match expression" to describe this but I don't actually use the $match operator. According to the docs, the selector should conform with $match's syntax, though the $match keyword is apparently not necessary in the actual expression.
Update 2: In the actual collection, outerField represents message, fieldA represents fansNo, and fieldB represents sharedNo. So outerField.fieldA represents message.fansNo and outerField.fieldB represents message.sharedNo. This is a stringified representation of the updateDescription field when the trigger fires (i.e. when I only specify updateDescription.updatedField in the match expression):
"updateDescription: {\"removedFields\":[],\"updatedFields\":{\"someOtherField\":310,\"message.fansNo\":1,\"updatedAt\":\"2020-06-22T13:29:08.829Z\"}}"
================================================================
Original post:
So I can't understand why it fails to trigger when I specify message.fansNo and message.sharedNo in the match expression.
I am setting up a database trigger on updates to a collection, but I'm not able to get my $match expression to work in filtering the change events that cause the trigger to fire. I want to fire the trigger only if one or both of 2 nested fields are present, say fieldA and fieldB. These 2 fields are nested inside an object, and the object is the value of a field in each document. Something like this:
// CollectionA schema
{
_id: ...,
outerField: {
fieldA: 1 // or any number
fieldB: 2 // or any number
},
...
}
I have tried using this $match expression below, but the trigger doesn't fire:
{
"$or": [
{
"updateDescription.updatedFields.outerField.fieldA": {"$exists":true}
},
{
"updateDescription.updatedFields.outerField.fieldB":{"$exists":true}
}
]
}
If I remove outerField.<field>, it works. That is:
{
"$or": [
{
"updateDescription.updatedFields": {"$exists":true}
},
{
"updateDescription.updatedFields":{"$exists":true}
}
]
}
But of course that's not useful to me because the trigger will fire on any update at all.
I would provide a demo but I'm not sure how to create a sample that has database triggers configured.
Any help will be appreciated, thanks!
So I was able to get around this problem by changing the query to watch for a field that gets updated at the same time but isn't nested. I think the problem with checking for a nested field is that the ChangeEvent's updateDescription property doesn't contain the actual nested object that has changed; instead it contains the dot-notation representation of the change. So if you look at Update 2 in my post you'll see that updatedFields has this value: {\"someOtherField\":310,\"message.fansNo\":1... instead of {\"someOtherField\":310,\"message\":{\"fansNo\":1.... By using message.fansNo in the $match query, Mongo will look for this object shape: {\"message\":{\"fansNo\":1..., which doesn't match in this case. A "real" solution here could be to escape the . in message.fansNo in my match expression, but I couldn't get that to work (see this thread).
So the "solution" that worked for me is really just a workaround that works for my specific use-case: it so happens that someOtherField is always updated along with message.fansNo, and someOtherField isn't nested. So I can match someOtherField without worrying about nesting. Basically this match expression gives me the results I want:
{
"$or": [
{
"updateDescription.updatedFields.someOtherField": {"$exists":true}
},
{
"updateDescription.updatedFields.someOtherField":{"$exists":true}
}
]
}
Hope this helps someone else!
Alright, so I have a collection called Polls. Inside the Polls "table" there is an attribute called choiceObjects which is an array of objects. Each object inside this array has its own attributes. What I need to do is update one of the attributes there. Ill give you a screen shot so you can better visualise what Im talking about
As you can see the choice objects have attributes like body, country etc. There is another attribute called pollid which is set to optional and therefore you cant see it right now. I need to update this pollid attribute now that I have acess to the pollid
Polls.update(
{ _id: pollId },
{ "$set": { "choiceObjects": { pollid: pollId } } }
); //this is kind of what Im trying to do but this isnt right
Since then... I have further tried the following :
var selectedpoll = Polls.findOne(pollId);
console.log(selectedpoll);
//Polls.update( selectedpoll, {"$set"{'choiceObjects.$.pollId':pollId}},false, true );
but when i try that i get the error : the positional operator did not find the match needed from the query. unexpanded update: choiceObjects.$.pollId
If I understand your objective correctly, you want to update (or add) pollid to all objects in the choiceObjects array. Unfortunately $, $push, $addToSet only work with single elements AFAIK.
This might not be what you are looking for but one possible and very obvious way to approach this problem would be to update the entire array in the collection i.e.
var choiceObjects = Polls.findOne({_id: pollId}).choiceObjects;
for (var i = 0; i < choiceObjects.length; i++) {
choiceObjects[i].pollid = pollid;
}
Polls.update({_id: pollid}, {choiceObjects: choiceObjects});
I want to make a publication with several additional fields, but I don't want to either use Collection.aggregate and lose my publication updates when the collection change (so I can't just use self.added in it either).
I plan to use Cursor.observeChanges in order to achieve that. I have two major constraints:
I don't want to publish all the documents fields
I want to use some of the unpublished fields to create new ones. For example, I have a field item where I store an array of item _id. I don't want to publish it, but I want to publish a item_count field with the length of my field array
Here comes the approach:
I plan to chain find queries. I never did that so I wonder if it possible. The general (simplified) query structure would be like this: http://jsfiddle.net/Billybobbonnet/1cgrqouj/ (I cant get the code properly displayed here)
Based on the count example in Meteor documentation, I store my query in a variable handle in order to stop the changes notification if a client unsubscribes:
self.onStop(function () {
handle.stop();
});
I add a flag initializing = true; before my query and I set it to true just before calling self.ready();. I use this flag to change my itemCount variable only if it is the publication is initialized. So basically, I change my switch like that:
switch (field) {
case "item"
if (!initializing)
itemCount = raw_document.item.length;
break;
default:
}
I wanted to check that this approach is good and possible before committing into big changes in my code. Can someone confirm me if this is the right way to go?
It's relatively easy to keep fields private even if they are part of the database query. The last argument to self.added is the object being passed to the client, so you can strip/modify/delete fields you are sending to the client.
Here's a modified version of your fiddle. This should do what you are asking for. (To be honest I'm not sure why you had anything chained after the observeChanges function in your fiddle, so maybe I'm misunderstanding you, but looking at the rest of your question this should be it. Sorry if I got it wrong.)
var self = this;
// Modify the document we are sending to the client.
function filter(doc) {
var length = doc.item.length;
// White list the fields you want to publish.
var docToPublish = _.pick(doc, [
'someOtherField'
]);
// Add your custom fields.
docToPublish.itemLength = length;
return docToPublish;
}
var handle = myCollection.find({}, {fields: {item:1, someOtherField:1}})
// Use observe since it gives us the the old and new document when something is changing.
// If this becomes a performance issue then consider using observeChanges,
// but its usually a lot simpler to use observe in cases like this.
.observe({
added: function(doc) {
self.added("myCollection", doc._id, filter(doc));
},
changed: function(newDocument, oldDocument)
// When the item count is changing, send update to client.
if (newDocument.item.length !== oldDocument.item.length)
self.changed("myCollection", newDocument._id, filter(newDocument));
},
removed: function(doc) {
self.removed("myCollection", doc._id);
});
self.ready();
self.onStop(function () {
handle.stop();
});
To solve your first problem, you need to tell MongoDB what fields it should return in the cursor. Leave out the fields you don't want:
MyCollection.find({}, {fields: {'a_field':1}});
Solving your second problem is also pretty easy, I would suggest using the collection helpers packages. You could accomplish this easily, like so:
// Add calculated fields to MyCollection.
MyCollection.helpers({
item_count: function() {
return this.items.length;
}
});
This will be run before an object is added to a cursor, and will create properties on the returned objects that are calculated dynamically, not stored in MongoDB.
In mongo I have a collections with records. These record are very complex. Now I would like to duplicate one of them.
I can easily select the one
mongo> var row = db.barfoo.find({"name":"bar"});
Now I actually don't know what to do. I don't know what is in row because I cannot find a way to print its content. How can I change specific properties and finally insert this modified row again
mongo> db.barfoo.insert(row);
thnx
You must change value _id - generate new:
var row = db.barfoo.findOne({"name":"bar"});
row._id = ObjectId();
db.barfoo.insert(row);
Good Luck!
I am going to assume that you're working directly inside the mongo shell.
Once you have your document (not a row :P ), you'd modify the properties in the same way you would a normal JavaScript object:
var doc = db.barfoo.findOne( { "name": "bar" } );
doc.name = "Mr Bar";
Note that the find() command returns a cursor, so if you're looking to extract a single document, you should use the findOne() function. This function returns a single document.
If you are interested in duplicating numerous documents, you can use the find() function and iterate over the cursor to retrieve each document:
db.barfoo.find( { "name": "bar" } ).forEach( function( doc ){
doc.name = "Mr Bar";
}
After you change the relevant properties, you can use the insert/save methods to persist the data back to mongo. Don't forget to change/delete the _id attribute so that you'll actually create a new document.
As a side note, in order to view the contents of an object in the mongo shell, you can use the print() function. If you want a more visually appealing output, you could use printjson().